1. Field of the Invention
The present invention is generally in the field of semiconductors. More particularly, the present invention is in the field of circuit element calibration.
2. Background Art
The proliferation of wireless communication devices has led to significant technological advances in the analog circuitry used in transceivers, converters, phase-locked loops and variable gain amplifiers, for example. Many of the advances have involved reducing the size, complexity and cost of each device, as well as reducing their power consumption. However, as the field has become more populated, precision in the manufacturing and operation of these devices has become increasingly important. For example, a cell phone transceiver must be capable of transmitting and receiving on precise channels within an available frequency band. In order to select specific channels, the cell phone must be able to precisely tune its transceiver so as to minimize cross talk with other transmissions.
In order to meet the requirements of low cost, low complexity and small size, many semiconductor manufactures choose to leverage conventional and relatively inexpensive fabrication technology, such as that used to form polysilicon resistors (polyresistors) in semiconductor devices, for example. But, as is known in the art, the actual resistance of a conventionally formed resistor can vary significantly from its desired resistance, from wafer to wafer and from process-run to process-run, increasingly as the size of a resistor is scaled down. Moreover, the actual resistance of a conventionally formed resistor can vary significantly with temperature. Fortunately, conventional resistors that are formed together on a single wafer often exhibit the same type of variance from their desired resistance. So, by measuring the resistance of one exemplary resistor on a single chip or die, one can calibrate all similarly fabricated resistors across a single-die semiconductor device, thereby providing the precision required by modern semiconductor devices.
Conventional calibration methods, which often require connections to off-chip devices, are typically expensive, complex, and time-consuming to implement. For example, one conventional method uses a relatively slow iterative process to match the resistance of an on-chip variable resistor block to that of an off-chip reference resistor. The external reference resistor can be relatively expensive to fabricate, and there is additional expense both in providing a precision via or pin on the semiconductor device for a precision analog electrical connection, as well as in providing sufficient mounting space and electrical noise shielding for the reference resistor.
Thus, there is a need to overcome the drawbacks and deficiencies in the art by providing a simplified, inexpensive, and more time-efficient system for calibrating resistors in semiconductor devices.